The technology of the disclosure relates to distributed antenna systems configured to provide communications signals over a communications medium to and from one or more remote units for communicating with client devices.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.
Distributed antenna systems (DASs) are effective when deployed inside buildings or other environments where client devices may not otherwise receive radio-frequency (RF) signals from a base station or other source. DASs can be used to provide coverage for applications such as public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses. A typical DAS establishes a number of RF antenna coverage areas, also referred to as “antenna coverage areas.” The antenna coverage areas are formed by remotely distributed antenna units (RAUs), which are sometimes referred to as remote units (RUs). A number of remote units are arranged to create an array of relatively small antenna coverage areas, with each RAU typically accommodating a small number of wireless client device users. This arrangement thus provides a uniform high quality signal and high throughput for wireless users.
Time-division duplexing (TDD) refers to duplex communication links where uplink is separated from downlink by the allocation of different time slots in the same frequency band. In TDD, users are allocated time slots for uplink and downlink transmission. When a DAS serves TDD wireless protocols, it must identify whether a radio source is transmitting (i.e., is in TDD Tx mode) or receiving (TDD Rx mode) and toggle its transmit/receive circuits accordingly. Conventional WiFi systems using TDD, for example, determine whether to toggle to TDD transmit (Tx) mode or stay in TDD receive (Rx) mode based on the output of a power detector that senses the power level at the radio port side of the DAS.
In this regard, FIG. 1 illustrates one such conventional system coupled to a radio source 10, such as a base station or transceiver. In FIG. 1, a TDD DAS head end 12 of a DAS 14 is provided. The TDD DAS head end 12 may also be a TDD repeater. The TDD DAS head end 12 receives TDD communications signals 16 in the form of TDD downlink communications signals 16D from the radio source 10 and provides TDD uplink communication signals 16U to the radio source 10. In the TDD DAS head end 12, a power detector 18 senses the power level of TDD communications signals 16 at the radio port side of the TDD DAS head end 12 to determine whether to toggle to TDD transmit (Tx) mode or stay in TDD receive (Rx) mode. The default status of the TDD DAS head end 12 is TDD receive (Rx) mode, where the DAS 14 is set to transfer signals in the uplink direction. When the power detector 18 detects power of the TDD communication signals 16 above a certain threshold, the assumption is that the power is sourced from TDD downlink communications signals 16D received from the radio source 10. This is because the power of the TDD downlink communications signal 16D is typically lower (e.g., 30-40 dB lower) than the power of the TDD uplink communications signals 16U due to loss. In response to the power detector 18 detecting power of the TDD communications signals 16 above a certain threshold, the TDD DAS head end 12 toggles input switch 20 and antenna switch 22 to TDD transmit (Tx) mode, where its circuits are set to transfer signals in the downlink direction.
One of the drawbacks of the DAS 14 in FIG. 1 is that the power generated by a receive (Rx) Amp 24 can leak through the directional coupler 26 to the power detector 18. For example, the directional coupler 26 may only have a directivity of up to 15 or 20 dB, but the difference in power between the TDD downlink communications signals 16D and the TDD uplink communications signals 16U may be greater than the directivity capability of the directional coupler 26. If power leaking from the receive (Rx) Amp 24 is high enough, it can cause the level comparator 28 to toggle the input switch 20 and the antenna switch 22 from TDD receive (Rx) mode to TDD transmit (Tx) mode even when the radio source 10 is not transmitting.